Many electronic devices such as mobile phones have illuminated regions such as keypads. These regions are often illuminated by an electroluminescent (EL) panel that actively lights up across its surface when an electric current is passed through it. For example, a keypad having partially transparent graphics or icons may be placed above the EL panel so that the icons are illuminated by the EL panel underneath.
In devices having multiple regions to be independently illuminated, each region is typically illuminated by a separate EL panel. However, the EL panels have non-illuminating strips along the edges allowing for electrical connections. These non-illuminating strips prevent adjacent regions from being placed in close proximity. Furthermore, each EL panel is powered by a high voltage driver, so each independently illuminated region requires an additional high voltage driver, increasing the cost, complexity and size of an electronic device.
One solution to independently illuminating a multiple regions of an electronic device is the use of a light guide made of a sheet of a substantially transparent material, with one or more light sources illuminating the sheet. Regions to be independently illuminated are separated by a slit in the light guide. However, if the light guide is prevented from lying flat in the electronic device, bulges in the light guide near the slits can cause light to bleed from one region to the next.